Previously, many types of indicators have been used in endeavoring to provide an effective means to monitor and indicate that a water filter is near or at the end of its useful life and needs to be replaced.
A cursory search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however Kurth et al. in U.S. Pat No. 5,188,727 teaches a water filter unit that has a pair of change water filter indicators, one for each filter cartridge, consisting of discs mounted on a post which are marked in months and years and may be set manually when the filters are changed. The indicators are mounted behind the cover with only the pre-set month and year visible from the outside.
U.S. Pat. No. 5,190,643 issued to Duncan et al. is for a portable water treatment device which uses a vessel with a replaceable filter cartridge inside. A lid has an aperture that communicates with the filter and a gate member that is reciprocally movable between a position closing the aperture in the housing and a position opening the aperture. In the open position water is poured into the filter cartridge through the aperture. An indicator moves one increment during a cyclic movement of the gate member which is limited to a predetermined number of increments preventing further movement when the filter needs to be changed.
Boldt Jr. et al. in U.S. Pat. No. 5,328,597 disclose an electronic unit for monitoring the number of uses of a filter cartridge. This unit is self contained and may be attached to any device that incorporates a water filter. A programmed integrated circuit uses different audio input signals to detect each use of the device and monitors when the device is operational and when the end of the life of the filter is eminent. The integrated circuit is programmed to operate a transducer to produce output signals during each use of the device informing the user that the device is operational, that the predetermined end of the filters useful life is eminent or that its life has expired. The unit includes a battery for supplying power to the transducer and integrated circuit and signals are visualized by light emitting diodes.
Parise in the recently issued U.S. Pat. No. 6,024,867 teaches a counter top water filter unit that includes a carbon particle filter cartridge for filtration. A replaceable electronic display monitor unit is mounted in an outlet housing fitted to the top of the cylindrical filter housing. The state of the life span of the filter cartridge is shown on the display monitor in terms of colored indicator lights which denote whether the filter cartridge is within, nearing an end or outside its expected life span. A green light indicates that the cartridge is in its usable life, a yellow light indicates it is about to reach its predetermined life span and a red light designates that the life span has been reached. The electronic circuit detects the time it takes for a ball to flow through a flow channel that is an integral part of the water flow circuitry thereby comparing this lapsed time to the equivalent amount of water passing through the filter. The solid state circuitry translates this information to the volume of water filtered which determines the life expectancy of the filter cartridge.
Other prior art, common to water pitchers with filters utilize floats and mechanical gears to slide a radial indicator a given direction each time the vessel is filled to its nominal level indicating that the filter should be changed when a pointer has completed its travel.